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Ultraviolet light occurs in three wavebands. UV-A is the longest waveband (>315 nm) which is close to visible light and is of limited biological significance. UV-B (280–315 nm) is damaging and mutagenic to living organisms. UV-C (

Vegetational history can help us to predict future environments by providing data for testing AGCMs, for indicating the vegetational response to rapid warming and changing CO2 concentrations, and for mathematical modelling of vegetation. Most of the data are palynological, and there are well over 100 pollen diagrams from tropical regions. Maps are presented showing summarized pollen diagrams from the lowlands of South-East Asia and the West Pacific, Tropical Latin America and Tropical Africa. In all these regions there is some evidence suggesting that at the LGM lowland forests were somewhat restricted in area and included montane elements. This is consistent with cooler and drier climate at the LGM. From the montane and lowland areas of these three regions, the pollen evidence is summarized in altitudinal diagrams. These suggest considerable depression of altitudinal zones at the LGM, suggesting temperatures c. 5–10°C cooler than now. These results conflict with earlier oxygen isotope data from marine foraminifera, but do not conflict with more recent oxygen isotope measurements from tropical corals. It is also suggested that altitudinal movements may be partly controlled by CO2 concentration and ultraviolet light.

As usually defined, the Massenerhebung or mountain mass elevation effect means the occurrence of physiognomically and sometimes floristically similar vegetation types at higher altitudes on large mountain masses than on small isolated peaks, especially those in or near the sea. Although the effect was first reported in the European Alps (Schroeter 1908) and in North America (where it is known as the Merriam Effect; Martin 1963), it is best known in the tropics. Perhaps its clearest expression is the occurrence of tropical mountain cloud forest (TMCF) (upper montane rain forest) at lower altitudes on isolated peaks than on the main mountain masses, which are taken as the norm (Figure 1).

Stratigraphies and pollen analyses are reported from three sites within 25 km east and west from Wabag in the highlands of Papua New Guinea, namely: Sirunki, 2500 m above sea level, 32000 to 1500 yr Inferred Ages; Inim, 2500 m above sea level, 10000 to 0 yr Inferred Ages; Birip, 1900 m above sea level, 2300 to 0 yr Inferred Ages. Events evidenced by these data are described against a time scale of Inferred Ages (I.A.) based on radiocarbon dates and stratigraphic considerations. The pollen analytical data from Sirunki are presented in terms of pollen recovery (deposition) rates as grains per square centimetre per year (grains cm-2a-1) and their interpretation controlled by information about total pollen deposition rates and differential pollen production and transport at the present day. Around Sirunki, the composition of the vegetation before 27500 I.A. is enigmatic, although almost certainly it was treeless. From then until 9000 I.A. subalpine and alpine conditions dominated except during two short periods when forest taxa grew in the catchment. Final afforestation began about 9000 I.A. but the composition of the forest did not stabilize until about 3000 years later. This relative stability was shortlived; soon after 5000 I.A. fluctuations in forest composition began. These fluctuations were associated with periodic changes in the proportion of forested to unforested land. The Inim data lead to conclusions generally compatible with those drawn from Sirunki. However, data from the two areas differ in detail, particularly in the later onset of change in the local forests about 2000 I.A. and its intensification, coeval with a diminution in forest area, after 500 I.A. The short record from Birip is dominated by serai changes on the crater wall itself but the main indicators of forest disturbance and unforested areas were already there at its beginning (2300 I.A.). It seems likely that general forest destruction began, or gained greater impetus, around Birip about 450 I.A. In the most general terms, the forest taxa, recorded by pollen analysis, have behaved consistently with their present distributions and ecological relationships throughout the last 30000 years. More detailed resolution, however, exposes many deviations from this generalization. The majority of taxa are usually associated in groups which vary in their composition repeatedly during a few thousand years, yet some of the taxa occasionally behave entirely individualistically. The establishment of forest broadly comparable with that growing around Sirunki today began about 9000 I.A., when the main components entered the catchment, but took about 2500 years to achieve balance and a repeated regeneration process. About 4500 I.A., the relationship between forest canopy trees and forest ephemerals changed from one explicable in terms of the latter’s role in natural forest regeneration to one suggestive of the ephemerals’ wide spread through the forest which could only have been achieved by degradation of the canopy. It is suggested that a rise in the Sirunki basin’s water level and the destruction of the surrounding forest about 13500 I.A. may have been due to seismic activity. The failure of the forest to re-establish there until 9000 i.a. was perhaps due to continued earth movement and partially to climatic conditions. The vegetation record from Sirunki suggests that the mean annual temperature there was similar to that of today between 27000 I.A. and 25500 I.A. but fell irregularly thereafter until between 18500 I.A. and 16000 I.A. it was probably about 10 °C below present. The mean annual temperature rose rapidly after 16000 i.a. and was within 1 °C of its present level by 13500 I.A. The cold episode between 18 500 I.A. and 16000 i.a. corresponds with the last glacial maximum at higher altitudes in New Guinea. Pollen analytical evidence of the altitude of the forest limit and Climap Project Members (1976) estimates of sea surface temperature at that time suggest a temperature lapse rate of about 8.5 °C per 1000 m altitude (compared with 5.8 °C at present), with a firn line kept high, as the geomorphological evidence demands, by low precipitation at high altitudes. In this coldest period the altitudinal forest limit was about 1500 m below its present level of 3800 m. There is some evidence to suggest that the highest altitude forests of that time may have been quite different from those of today, perhaps containing components of the lower mountain forest canopy as well as the plants of the present upper mountain forest. This implies that the upper mountain forest becomes a separate entity only during comparatively short excursions up the mountains during periods of relatively warm climate. The low altitude of the forest limit during the last major cold period and its subsequent rise through 1500 m must have had substantial repercussions on the composition of the forests at lower altitudes. Although there is no archaeological evidence, the pollen analytical data suggest human interference with the forests around Sirunki from about 4300 I.A., which for 1300 years involved clearing of the forest and the enhanced growth of ephemerals of forest and open-land. Subsequently, the forest remained generally degenerate and a new wave of clearing began about 2000 I.A. near both Sirunki and Inim which continued and intensified about 500 I.A. At the lower altitude of Birip, forests were already disturbed by the beginning of the pollen analytical record at about 2300 I.A.

Easter Island is the most isolated piece of inhabited land in the world. It exhibited an unique megalithic culture1–3, involving the sculpting of giant statues (moai) especially between AD ∼1400 and ∼16804 when, for unknown reasons, the culture suddenly collapsed. The island is also of interest in relation to Pleistocene climatic change as CLIMAP5 predicted no reduction of sea-surface temperatures for this part of the Pacific at 18,000 yr BP. We have obtained fossil pollen records covering the past 37,000 yr from three craters on the island. They suggest that the late Pleistocene climate was cooler and/or drier than the present one. They also suggest the former existence of forest on the island, and its decline in the last millennium. This decline was probably due to deforestation by man and could have caused the cultural collapse.

Summary Two complementary pollen diagrams from Canna show a forest history similar to that found elsewhere in north-west Scotland, but the NAP values are unusually high. A late-glacial may possibly be present.

The former existence of palms on Easter Island has been demonstrated palynologically1,2, but the genus could not be determined from pollen morphology. We now report the discovery on the island of endocarps (shells) from palm fruits which appear to bethose of an extinct species related to the Chilean ‘wine palm’, Jubaea chilensis (Molina) Baillon. The endocarps, found in caves, have all been gnawed by rodents, which could have helped to make the species extinct. The radiocarbon age of the endocarps is 820 ± 40 yr BP, which falls within the phase during which deforestation occurred on the island2 and the giant statues (moai) were erected1,3. Decline of the palm could have contributed to the decline of the moai culture.

Tansley1 erected the hypothesis that the grasslands of the British chalk were the product of neolithic human forest clearance although he did not discount the possibility that in some areas the grasslands might have persisted throughout the forest period. Pigott and Walters2 suggested a range of calcareous habitats where forests perhaps failed to form a closed canopy: where erosion was rapid, slopes steep, or soils too thin for trees to root. Despite these exceptions, most authors describe chalk grasslands as the product of neolithic clearance (for example, refs 3 and 4). The debate has been starved of evidence until now by the almost total lack of Flandrian botanical data from sites actually on the chalk. Here we summarize the results of a broad palaeoecological study (using pollen, and plant and animal macrofossils) of a site in the heart of the Yorkshire Wolds which has yielded the first late-glacial and early Flandrian pollen record from the British chalk5. This deposit has provided evidence of early Flandrian chalk grasslands and of their persistence throughout the Pre-Boreal and Boreal periods.

Polleniferous sediments from SE Asian lakes and swamps may reflect anthropogenic changes in their surroundings. Increases in the abundance of pollen of secondary forest trees, herbs and crop plants are possible indicators of human activity, as are evidence of soil erosion and presence of charcoal. The areas most studied so far are Sumatra and New Guinea. Sites in Sumatra show forest disturbances from 4000 BP or earlier: possibly 7000 BP. From about 2000 BP permanent clearings appear. In New Guinea there is forest clearance in the highlands from c. 5000 BP or earlier, disturbance of swamps back to c. 9000 BP, and evidence of burning from c. 10,000 BP. Man has been practising forest disturbance in SE Asia for thousands of years, and this has led to ecological degradation.

Late Quaternary pollen records are described from two swamps at c. 1500 m a.s.l. in the Sumatran Highlands. At Danau di Atas (DDA) the record extends back to c. 31,000 BP. At Telago (TEL) the record extends back to c. 9000 BP. The results suggest that, in the Late Pleistocene, vegetation zones were depressed, and a gymnospermrich rainforest, now found only above 1800 m, surrounded DDA. At times upper montane forest may have been close to the site, suggesting a vegetational depression of c. 800 m. Mean annual temperature may have been c. 1.6?C to c. 5.2?C cooler than now. There is no direct evidence of formerly drier climates, although a possible reduction of water levels in the Late Pleistocene is suggested. During the Holocene, there is evidence for disturbance of rainforests, possibly by man, from a date some time after c. 8200 BP. Extensive recent forest clearance is demonstrated.

There are at least three reasons for suspecting the vegetation of the New Guinea Highlands to be changing. Firstly, forest is being actively cut down by the New Guineans to make gardens and it has even been suggested (Robbins 1960) that almost all the non-forest (i.e. vegetation other than forest) is anthropogenic. Secondly, there is geomorphological evidence of a lower snowline formerly in New Guinea (Dozy 1937; Reiner 1960; Bik 1967) and the vegetation may therefore have been influenced by long-term climatic changes. Thirdly, New Guinea is subject to tectonic disturbance and volcanic activity (Taylor 1957), which may have had vegetational repercussions. Previous ecological work in the Highlands has been mostly restricted to general ecological surveys (e.g. Robbins 1958; Robbins & Pullen 1965) and to more detailed studies of small areas (Walker 1966, 1968). The present paper reports mainly random sampling of all vegetation within the Wabag region, including the 'montane' rain forest, and analysis of the data by computer techniques for classification and ordination. This contrasts with recent numerical analyses of rain forest (Ashton 1964; Webb et al. 1967a, b; Greig-Smith, Austin & Whitmore 1967) which have all been carried out on data collected from subjectively sited plots in lowland forest.